Radiation based systems for screening people and in use today at transit points, such as airports, courthouses, etc., are generally portal systems that are bulky and not conducive for portable applications. Unfortunately, such prior art screening systems are not compact enough (example, have heavy back-end cables and wires for connecting the photomultiplier tubes to a centralized analog-to-digital conversion and power station) and are often difficult and time-consuming to use and/or transport.
Also, security systems are presently limited in their ability to detect contraband, weapons, explosives, and other dangerous objects concealed under clothing. Metal detectors and chemical sniffers are commonly used for the detection of large metal objects and certain types of explosives, however, a wide range of dangerous objects exist that cannot be detected using these devices. Plastic and ceramic weapons increase the types of non-metallic objects that security personnel are required to detect. Manual searching of subjects is slow, is inconvenient, and would not be well tolerated by the general public, especially as a standard procedure in high traffic centers, such as at airports.
It is known in the art that images of various types of material can be generated using X-ray scattering. The intensity of scattered X-rays is related to the atomic number (Z) of the material scattering the X-rays. In general, for atomic numbers less than 25, the intensity of X-ray backscatter, or X-ray reflectance, decreases with increasing atomic number. Images are primarily modulated by variations in the atomic number of the subject's body. Low-Z materials present a special problem in personnel inspection because of the difficulty in distinguishing the low-Z object from the background of the subject's body which also has low-Z.
Known prior art X-ray systems for detecting objects concealed on persons have limitations in their design and method that prohibit them from achieving low radiation doses, which is a health requirement, or prevent the generation of high image quality, which are prerequisites for commercial acceptance. An inspection system that operates at a low level of radiation exposure is limited in its precision by the small amount of radiation that can be directed towards a person being searched. X-ray absorption and scattering further reduces the amount of X-rays available to form an image of the person and any concealed objects. In prior art systems this low number of detected X-rays has resulted in unacceptably poor image quality.
This problem is even more significant if an X-ray inspection system is being used in open venues such as stadiums, shopping malls, open-air exhibitions and fairs, etc. At such venues, people can be located both proximate to and/or at a distance from the machine. If a person being scanned is not very close to the X-ray machine, the resultant image may not be clear enough since the amount of radiation reaching the person is very low. This limits the range of scanning of the system to a few feet from the front of the machine. If, however, a person being scanned is too close to the X-ray machine, the amount of radiation impinging on the person may not be safe.
Further, X-ray screening systems deployed at airports in the United States of America (U.S.A.), for performing automatic threat detection, have to comply with guidelines set by the Transportation Security Administration (TSA). Current TSA guidelines require being capable of scanning a person at least 6 feet 6 inches tall from elbow to elbow which translates into a scanning width of at least 103 centimeters. Also, given the increasing rush at the airports, a screening system deployed at an airport or other such heavy throughput areas must provide a fast scanning time, preferably ranging around 10 seconds per scan. Yet further, a screening system should preferably be compliant with laws governing disabled persons. In the U.S.A the screening systems must be compliant with the regulations set forth in the Americans with Disabilities Act (ADA).
Therefore, there is a need for a compact radiographic detector/source screening system that has improved detection efficiency, is light yet sufficiently rugged and can be easily unassembled for transportation and then is simple to reassemble at a site.
Also is required a screening system that may be deployed easily by virtue of modularity, smaller size, reduced weight and rapid assembly; while at the same time provide a higher scan speed (higher personnel throughput), and the latest processing electronics.
There is also a need for a radiographic screening system that provides good resolution as well as large range of view and fast scanning speed, while keeping the radiation exposure within safe limits. That is, the system should not only be safe for people at close distances, but also provide a good resolution and penetration at standoff distances. In particular, conventional systems have been unable to generate the requisite field of view (scanning a person of a predefined height and width), at a predefined distance from the inspection system, at the required scan speed at an acceptable radiation exposure level to yield an acceptable resolution level.